Digital oscilloscopes have limited input bandwidths. The bandwidth of an input signal is limited to the input bandwidth of the oscilloscope. In U.S. Patent Application Publication 2004/0128076 to Pupalaikis, et al., a real-time oscilloscope is disclosed with an increased usable bandwidth. The real-time oscilloscope splits the input signal into multiple split signals. One split signal is digitized. Simultaneously, the other split signals are frequency shifted to a baseband signal and digitized. The digitized frequency-shifted signals are frequency shifted to their original frequency range, and then combined with the other digitized signal to create a representation of the input signal. By frequency shifting frequency bands of the input signal to be within the bandwidth of their respective digitizers, an input signal having a frequency range larger than the input bandwidth of a digitizer may be acquired using the lower bandwidth digitizers.
However, this real-time oscilloscope requires that the input signal be split by a splitter and that the equivalent of an oscilloscope channel be used for each frequency band used in creating the representation of the input signal. As a result, the input signal may be degraded by the splitter, and the cost of such a single increased bandwidth oscilloscope channel increased to approximately the number of frequency bands times the cost of a normal channel.
Accordingly, a need remains for an improved acquisition apparatus for use in test and measurement instruments.